Cement softener and process of using the same



Patented Jan. 2, 1945 UNITED; STATES PATENT orrlcs CEMENT SOFIENER AND PROCESS OF USING THE SAME Earle o. Pitman, Red Bank, N. 1., assignor to n. I. du Pont dc Nemoura & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application August 1, 1942,

. Serial No. 453,233

' ISCIa-ims. (01.154-40) Th s invention relates to improvement in adhesively joining surfaces and more particularly to a composition and method for activating a dried cellulose derivative film on the surfaces to be Joined. The invention is particularly adapt ed to the-manufacture of'shoes.

.This application is a continuation-impart of my co-pending application 8. N. 380,456, filed February 25, 1941.

En themanufacture of footwear of all kinds, it has been common practice to sew the sole to the upper either directly or through the medium" of a'welt. More recently, however, particularly in the manufacture of women's shoes, this method has been replaced by a process which consists in adhesively'joining the sole to the upper by means of a suitable cement which in the most important commercial practice con tains a cellulose derivative, usually cellulose nitrate. In operating this more economical process, the marginal area of the shoe sole and the overlasted portion of the upp i are roughened by bufiing or other suitable means and the adhesive applied to these areas by brushing or by mechanical extruding devices. After the adhesive composition has dried or hardened by the evaporation of volatile solvents contained in the composition, the parts can be stored until it isdesired to assemble them in the manufacture' of the complete shoe. At that time the cement on one or both of 'the parts (usually the cement on the sole only) is activated or softened by applying an active solvent composition to the surface of the cement and the parts then assembled in proper relation in a pressure device where they are. held under pressure until" the cement has dried and the parts thus securely Joined. V

The conventional active solvent compositions (usually called cement softeners or activators) consisting entirely of volatile ingredients or modified with a small quantity'of a. substantially non-volatile liquid material such as dibutyl phthalate or a solid ingredient such as cellulose nitrate, are characterized by several assembling the parts, then the time required in the pressure device to dry or harden the cement is excessive. Those-softener compositions containing a small proportion of solids ingredients as heretofore available are defective in that This invention has as the primary object the provision of a cement softener which when applied to a dry cement fllm prevents too rapid escape of activating solvents prior to assembling the parts and yet does not require excessive periods of dwell" in the pressure device to effect an acceptable bond between the parts to be joined. I

Another object of theinvention is the provision of a cement softener which is less susceptible to squeeze out between .the surfaces when pressure is applied to the parts being joined.

Another object is the provision of a cement softener which prevents staining or soiling of surfaces outside the cement coated areas.

Another object is the provision of a cement softener which can conveniently be employed with mechanical extruding devices for applyingthe softener to the dry cement film.

A furthenobiect is the provision of a process for cementing surfaceswhich eliminates skips and greatly improves uniiormityof the joint.

A further obiect is the provision of a process for cementing surfaces which affords substantial operating economies and reduces the numberof reiec due to faulty bonds such as are encountered in conventional practice.

defects which reduce the-emciency of the proc-- ess. In-some dnstances, skips (areas where the shoe parts are not effectively united) are encountered. In others, staining of the shoe uppers by migration of the softener from the area of application takes place. Also, if the softener consists of highly volatile materials in order to shorten the'time required for the assembled parts in the pressure device, there is not sumcient time to permit proper positioning of the parts and some areas may be dry before the unit is placed under pressure -so that there is no bond oronlyawcalrbondatthesepoints. IftliesoI- vents are adiustedto permit a longertime for active solvent for the dynamite cellulose nitrate and for the dried cement.

'The following examples are given by way of .A still further object is the provision of a cement softener which is particularly adapted for use in themanufacture of cemented shoes.

Other objects will appear as the description'of the: invention proceeds.

These objects are accomplished by means of animproved cement softener compositioncomprising dynamite cellulose nitrate dissolved in a liquid volatile vehicle containing at least one illustration only and no limitations are intended thereby except as indicated inthe appended claims.

Example I Per cent by weight Dynamite cellulose nitrate 1.3 First Acetone 20.0 portion- Diethyl ether 20.0

Denatured ethyl alcohol (23A)- 0.7

Second {Acetone 12.6 portion- Diethyl ether 45.4

The first portion is compounded in any suitable manner known in the art. After the nitrocellulose has dissolved, the second portion is added with stirring. With the dynamite cellulose nitrate commonly employed for coating purposes.

lose nitrate it is desirable to mix the composition somewhat longer than is-customary with conventional forms of cellulose nitrateinorder to insure a stable final viscosity.

The viscosity of this composition was 414 centipoises.

The cellulose nitrate used in this example was dynamite cellulose nitrate which is' commonly employed in the manufacture of explosives. It is characterized by an extremely high viscosity and gel structure in suitable solvents, -forexample, acetone. It differs from low viscosity or even so-called 1,000 seconds viscosity nitrocellulose (types which are available for general finishing and adhesive utility) by its gel structure or false body characteristic in solution and by the avoidance of any intentional treatment in its manufacture to reduce its viscosity character :the art. Cotton linters previously subjected to only a very mild digestion at atmospheric pressur to remove oils and fats are nitrated at a temperature of 0-5 C. for about 30 minutes with a nitrating acid mixture of which the following is typical:

The nitrogen content'of dynamite cellulose nitrate is usually between about 12.15 and 12.35%. The product has an exceptionally high viscosity characteristic and cannot be dissolved in volatile solvents and diluents in any considerable concentration. As an arbitrary (but necessary modification of the A. S. T. M. D-301-33) measure of the viscosity characteristic of this type of cellulose nitrate, the cellulose nitrate of Example I was dissolved in acetone in the proportion of 3% by weight. This is because a 12.2% solution as called for by the A. S. T. M. method could not be made. The viscosity of this solution determined in accordance with the modified' falling ball method was 95.2 seconds. A similar determination on a heavy coating type 13 Per cent Nitric acid 28.85

Sulfuric acid 56.91

Nitrosyl sulfuric 2.82

- Water v 16.42

The cement softener of Example I was employed in joining shoe sole leather strips (6" x 1" and about in thickness) by first applying a cellulose nitrate cement of the following composition to the previously buffed leather surface by brushing.

Example 11 Per cent by weight Cellulose nitrate (6 sec. A. S. T. M. Spec.

D-301-33 Formula A) 17.6 Dibutyl phthalate v 4.4 Isopropyl acetone 40.8 Butyl acetate 1.6 Hexane 20.6 Denatured ethyl alcohol 15.0

The cement coated leather strips were-allowed to thoroughly dry. The softener of Example I was then brushed uniformly over the dried cement film on thesurface of the leather strips. Pairs of the strips were then immediately placed in a conventional shoe cementing pressure device with the cement coated surfaces together and pressure applied at 50 pounds per square inch 1 for 3 minutes. With the ordinary liquid soften 'ers, the period of dwell in the pressure device required would be about 10 minutes. An examination of the strips after removal showed that a uniform bond had been secured without extrusion of any of the material tothe exterior surfaces of the strips. It was found that if due to application of excess softener, some small amount of softener reached the exterior surfaces, it could be readily and completely removed by a stiff bristle brush since the dried softener is quite brittle. The bond was uniformly strong over the entire area of the leather strips and no skips were observed. The joint strength was comparable to that obtained by conventional methods. There was no evidence of staining of exterior surfaces of the leather.

The extremely high viscosity characteristic of I the dynamite cellulose nitrate and the tendency of this material to quickly form a gel structure during evaporation of the volatile solvents in the softener composition are the basic factors which establishthe remarkable superiority of the new product for the uses indicated and distinctively set it apart from cement softeners heretofore available. Thus, the almost instantaneous setting up of a gel structure after application of the softener to a dried cement film traps the active volatile cellulose nitrate solvents and retains them on the surface of the cement film for a sufficient time to thoroughly activate the cement. Also, because of this unusual and unique property, excessive haste on the part of the operator in properly positioning the parts to be joined and placing them in a'pressure device is avoided. In

prior practice, unless the parts wer positioned quickly, the volatile solvents were sometimes dissipated from all or part-of the cement area before the parts were joined, thus causing faulty joints and an excessive number of rejects. The high viscosity characteristic of the dynamite cellulose nitrate is of particular advantage since it permits the use of much lower solids in obtaining the desired high' viscosity in the softener composition which aids .in preventing the migration of the softener to areas adjacent to the-cement coated areas, thus preventing staining and soiling of exterior surfaces. This property also greatly aids in the application of the softener, permitting the use of much lessskilled labor for thisoperation. Y

The viscosity of the softener composition is also important to the successful operation of the invention. This may be adjusted by varying the solids content of the softener, particularly the amount of dynamite cellulose nitrate used. Ingeneral, operable compositions may have a viscosity between about 100 and 1,500 centipoises (in certain instances the viscosity maybe somewhat higher) although it is preferable to employ compositions which have a viscosity of between about 100 and 500 centipoises. Operation within this preferred lower range of. vi'scosities is permitted directly because of the peculiar characteristics of the dynamite cellulose nitrate since the new properties are not found in any of the presently available commercial general utility cellulose nitrates included in the highest viscosity characteristic type, namely, the so-called 1,000 second cellulose nitrate.

' Due to the very high viscosity characteristic of the dynamite cellulose nitrate and its unique tendency to form a gel structure quickly at the start of the evaporation of thevolatile solvents when applied to acement surface, it is possible and quite desirable to use a lower solids contentthan has heretofore been possible with conventional cellulose nitrates in order to'obt'ain the high viscosity in the final composition .and to afford the trapping of solvents on the cement film. surface. Amounts of dynamite cellulose nidiluents, such as butylalcohol, diethyl ether, "aliphatic and aromatic hydrocarbons, may be used taking care that th active solvent portion of the volatile vehicle is present in suilicient quantity to insure complete solution of the cellulose nitrate. In general, it is preferred to use .so1-,

vents and diluent; which are highly volatile, that is, those with high evaporation rates in order to reduce the necessary time offdwell" in'the pres sure device to afford the required joint strength.

The use of plasticizers and compatible resins is also permissible insome cases but these materials, if included, should preferably be kept to a minimum so as to not detract from the su- Y perior' properties imparted by the dynamite cellu lose nitrate. It is also possible to include a minor proportion of a conventional coating type celluf which required markedly higher solids content to lose nitrate preferably of high viscosity but any appreciable quantities of such material tends to reduce the desirable improvements afforded by added if any should be small in order toavold adverse effects on the "false body" property which distinctively characterizes the dynamite cellulose nitrate.

The new cement softener is of general utility inthe activation of cements which may be softened or rendered tacky with the liquid vehicle containing the dynamite cellulose nitrate and is particularly useful in the manufacture of shoes for joining the shoe sole to the-upper. The invention is also, useful in the manufacture of leather belts such as those employed for power transmission, laminating plywood, joining Celluloid and other plastic objects, motion picture film, lacquered paper or lacquered regenerated cellulose sheeting and sealing cellulose derivative wrapping materials. The new compositions may be used in the fabrication of laminated paper containers from lacquer coated per and for joining the abutted' edges of carpe seams where cellulose nitrate cementsare commonly employed.

The invention may also be used in conjunction with the novel cementing methods disclosed in U. 8. Patents 2,283,946 and 2,087,480 which describe means for joining surfaces by vacuum and high frequency electrical treatments, respectively.

Various types of cements containing polymeric organicmaterials including cellulose derivatives,- for.example,'cellulose esters such as cellulose ni- .trate, cellulose acetate, cellulose butyrate, cellupermit accurate positioning of the parts to lose propionate and the mixed cellulose esters, cellulose ethers. natural resins and synthetic resins such as alkyds, vinyls, acrylic and methacrylic acid resins, and urea-formaldehyde resins may be activated or softened by the new softener provided only that such cements are dissolved or attacked by the liquid volatile vehicle of the compositions of the invention.

The invention offers numerous advantages which are of considerable practical and economic importance in the field of adhesively joining surfaces, particularly in the" manufacture of shoes.

Laborcosts are materially reduced since less adept operators may be employed because of the more fool-proof nature of I this new softener. Rejects attributed to faulty joints resulting from "skips in the step of applying the cement softener are avoided because a more uniform distribution of the softenerover the dried cement film is accomplished and because'the softener forms a gel which retains the volatile solvents for a suiiicient period (for 30 seconds and more) to be joined. However, the actual time required 'for eflecting the joint in the pressure device is reduced, thus speeding up production.

The

' softener may be applied manually with a brush or preferably with a mechanical extruding device which also contributes to the securing'of a more uniform joint because a more controlled application of the softener can be obtained with such device. Because of therapid formation of a gel after application of the softener, staining of the exterior of the parts to be joined is completely avoided. If any of the material isv extruded to the exterior surfaces, it can be readilyremoved with a stiff bristled brush. Another advantage resides in the high viscosity of the softener composition as obtained with appreciably. lower solids content as compared to softeners of similar type heretofore available obtain equal viscosity and which did not exhibit the dynamite cellulose nitrate and the amount tinctively sets the new products apart as greatly superior for the indicated purposes. Solvents of higher evaporation rates and greater proportions of such solvents can be used in the new compositions since the rapid formation of a gel structure traps the solvents and retains them until the parts are properly positioned but after the pressure is applied the-gel structure is broken and the highly volatile solvents are then rapidly dissipated. The peculiar nature of the composition also affords better control of the amount of softener applied, thus avoiding undue waste.

It is apparent that many widely difl'erent embodiments of the invention may be made without departing from the spirit and scope thereof, and

therefore, it is not intended to be limited except has a viscosity of from 40 to 200 seconds, and a liquid volatile vehicle containing at least one solvent for the said cellulose nitrate and the dry cement, the viscosity of the said composition being of the order of 100 to 1500 centipoises.

2. The composition of claim 1 in which the viscosity characteristic of the dynamite cellulose nitrate is about 95 seconds in a 3% solids acetone solution.

3. The composition of claim 1 in which the dynamite cellulose nitrate is present in amount between 0.7 and 1.5% by weight.

4. The composition of claim 1 in which the viscosity is between about 100 and 500 centipoises.

5. The composition of claim 1 in which the sole solids ingredient is dynamite cellulose nitrate.

6. The product of claim 1 having approximately the following composition:

' Percent by weight Dynamite cellulose nitrate 1 3 Acetone 20.0 Diethyl ether 20.0 Denatured ethyl alcohol (23A) 0.7 Acetone 12.6 Diethyl ether 45.4

consists of from 0.7 to 1.5% of dynamite cellulose 7. In the process of cementing surfaces wherein at least one surface is coated with a cement containing a polymeric organic material and allowed to dry before joining the surfaces, the improvement which comprises activating the dried cement with a composition comprising from about 0.2 to 2.0% by weight of dynamite cellulose nitrate a 3% acetone solution of which has a viscosity of from 40 to 200 seconds, and a liquid volatile vehicle containing at least one solvent for the cement, the viscosity of the said composition being of the order of 100 to 1500 centipoises.

8. The process of claim '7 in which the polymeric organic material is a cellulose ester.

9. The process of claim 7 in which the polymeric organic material is cellulose nitrate.

10. The process of claim 7 in which the cement is a cellulose nitrate cement and the liquid volatile vehicle in the softener contains a ketone.

11. The process of claim- 7 in which the viscosity characteristic of the dynamite cellulose nitrate is about seconds in a 3% solids acetone solution.

12. The process of claim 10 in which the dyna-' mite cellulose nitrate is present in amount between 0.7 and 1.5%.

13. The process of claim 7 in which the viscosity is between about and 500 centipoises. 14. The process of claim '7 in which the said composition is as follows:

15. A gelatinous composition suitable for activating dry cellulose derivative cements which nitrate said dynamite cellulose nitrate having a viscosity characteristic of between 40 and 200 seconds in a 3% acetone solution, about 32.6%

acetone and'the balance being an organic volatile non-solvent liquid for the said cellulose nitrate.

EARLE C. PI'I'MAN. 

